Interannual dynamics of precipitation concentration characteristics in mountainous small watersheds and attribution analysis of plum rain-typhoon interactions

To solve the difficulty in supporting fine-grained management of small and medium-sized watersheds with large-scale rainfall research, this study focuses on the Shunxi Watershed in Pingyang County, Wenzhou City. Based on rainfall data from 2010 to 2021, it integrates the indicators of Precipitation Concentration Degree(PCD) and Precipitation Concentration Period(PCP), combined with plum rain, and typhoon data, to analyze the interannual variability of rainfall spatiotemporal patterns caused by the plum rain—typhoon process. Results show:①The interannual variation of PCD is significant, while PCP exhibits periodic fluctuations, which are related to the potential impact cycles of large-scale climate oscillations;②The contribution rates of the plum rain and typhoons exhibit weak negative correlation with pronounced interannual fluctuations. The dominant type of either process regulates the characteristics of precipitation concentration;③The contribution ratio of plum rain and typhoons(MTI) showed a significant negative correlation with the peak rainfall timing. In plum rain-dominated years, peak rainfall occurred around mid-June, with stabilizing at 0.35～0.45, whereas in typhoon-dominated years, peak rainfall was delayed to late July. These findings reveal the dynamic mechanism governing rainfall concentration patterns in small-to-medium catchments under terrain-climate co-regulation, providing critical thresholds for disaster warning and model optimization.